Dell PowerVault MD 32XX/36XX Series Storage Arrays CLI Guide

Data replication between the primary virtual disk and the secondary virtual disk in a replication relationship is managed by the RAID controller modules and is transparent to host machines and applications. When the RAID controller module owner of the primary virtual disk receives a write request from a host, the RAID controller module first logs information about the write to a replication repository virtual disk. The RAID controller module then writes the data to the primary virtual disk. The RAID controller module then initiates a write operation to copy the affected data to the secondary virtual disk on the remote storage array.

If a link interruption or a virtual disk error prevents communication with the secondary storage array, the RAID controller module owner of the primary virtual disk transitions the replicated pair into an Unsynchronized status. The RAID controller module owner then sends an I/O completion to the host sending the write request. The host can continue to issue write requests to the primary virtual disk, but remote writes to the secondary virtual disk do not take place.

When connectivity is restored between the RAID controller module owner of the primary virtual disk and the RAID controller module owner of the secondary virtual disk, the virtual disks must be resynchronized by copying the blocks of data that changed during the interruption to the secondary virtual disk. Only the blocks of data that have changed on the primary virtual disk during the link interruption are copied to the secondary virtual disk.